1. Field of the Invention
The present invention relates to a resin composition which is usable for an exterior article without being coated on its surface when molded into the article and has an excellent color tone and good impact resistance and weatherability.
2. Description of the Prior Art
An impact resistance has heretofore been given to rigid resins by reinforcing them by elastomers. An ABS resin is a typical instance of the reinforced resin of this type, but since a diene type rubber is used as the elastomer component, the weatherability is poor and outdoor use of this resin is restricted. This defect can be moderated to some extent by addition of an ultraviolet absorber or antioxidant, but a significant improvement of the poor weatherability of the ABS resin cannot be attained by incorporation of such additive. Accordingly, at present, the weatherability of the ABS resin is improved by forming a plating or coating layer on the surface of the ABS resin so that the ABS resin can be used outdoors. However, the surface treatment of the ABS resin comprises many steps and a problem of environmental polution readily arise. Accordingly, development of thermoplastic resin composition which can retain excellent appearance, impact resistance and weatherability without formation of a plating or coating layer even if they are used outdoors for a long time has been desired in various fields where outdoor application is indispensable, for example, in the fields of automobiles and outdoor electric devices.
Various methods where a saturated rubber is used as the elastomer have been proposed as means satisfying the above desire. For example, an acrylic ester type rubber has been used, and many examinations have been made on this rubber. However, the acrylic ester type rubber is disadvantageous in that the speed of elastic recovery is lower than that of the diene type rubber. Accordingly, if a resin composition comprising such rubber and a rigid resin is subjected to injection molding, orientation of rubber particles is conspicuous and a pearl-like pattern is formed with the vicinity of the gate of a molded article being as the center, resulting in reduction of the appearance characteristic and decrease of the commercial value.
We made researches on formation of a pearl-like pattern which is caused by using an acrylic ester type rubber and found that if a cross-linked resin is made present in the interiors of particles of the acrylic ester type rubber, the above defect can be eliminated. We already filed a patent application for an invention based on this finding. Indeed, formation of a pearl-like pattern in the vicinity of the gate of a molded article at the injection molding step can considerably be controlled by this invention. However, as a result of our researches made afterward, it was found that when a colored molded article is prepared by injection molding by using a dye or pigment such as carbon black, color unevenness takes place with the vicinity of the gate being as the center because of an interference effect in a visible ray region which is due to orientation of the dye or pigment at the injection molding step, and this defect cannot be overcome by our previous proposal. If color unevenness takes place at the injection molding step, the color tone of the molded article becomes non-uniform and it is not suitable as an exterior article without being coated on its surface.